Cathode ray tubes are used widely in present technology. Cathode ray tubes (CRT) are used in television sets, word processing terminals, computer terminals, video games, and a variety of other applications. In all of these applications, the cathode ray tube is used to produce an image on a fluorescent screen.
A cathode ray tube consists of an evacuated glass container with a fluorescent screen at one end and a focused electron gun and deflection system at the other. When the electron beam emerges from the electron gun, it passes through pairs of metal plates mounted in such a way that they deflect the beam horizontally and vertically to produce a luminous pattern on the screen. The screen image is a visual representation of the voltages applied to the deflection plates. In addition to the screen image, the cathode ray tube also produces X-ray radiation that is emitted outwardly from the screen and outwardly from the body of the cathode ray tube. The amount of X-ray radiation produced from the cathode ray tube will vary in relation to the voltage in the power supply. In other words, color cathode ray tubes will produce a higher level of X-ray emission than will black-and-white cathode ray tubes.
In earlier days, it was believed that the amount of X-ray radiation produced by the cathode ray tube was relatively harmless to human beings. This was based on the fact that people were generally far removed from the cathode ray tube in its most common usage, i.e., as part of a television set. The diffusion of the X-rays over a distance greater than five feet generally exposes the viewer to minimal X-ray radiation. Also, in earlier days, cathode ray tubes did not have widespread application as word processing machines, computer terminals, or as video games.
Today, however, there is considerable evidence that the X-rays generated by a cathode ray tube present a considerable danger to human health. There is strong evidence that suggests that the emissions of cathode ray tubes can cause birth defects, premature births, and other genetic abnormalities. This is a relatively recent phenomenon. The main reason for this problem is the fact that users of the cathode ray tube are no longer far removed from the radiation source. Secretaries using word processing terminals remain seated in close proximity to the cathode ray tube for eight hours a day, and generally five days a week. Over time, this amounts to a very high level of exposure to the X-ray emissions. Moreover, users of video games can sometimes remain implanted in front of screens for equally long lengths of time. The chances of excessive exposure to radiation is magnified by the fact that video games are usually color cathode ray tubes. There are also many other occupations which require constant viewing of cathode ray tube screens. There has been very little effort to develop devices which prevent the radiation emission from cathode ray tubes. Heretofore, the need to develop such a radiation prevention device was thought unnecessary. Also, the technology was relatively unavailable for coupling radiation prevention with the clear viewing of the cathode ray tube screen.
The only device thought practical for preventing X-ray emission from cathode ray tubes was a clear lead (Pb) screen. Such a screen could be placed in front of a cathode ray tube and would effectively prevent any X-ray emission from traveling beyond the surface of the lead screen. Unfortunately, such clear lead screens are very impractical both from an economical standpoint and from a viewing standpoint. The cost of such screens is in the neighborhood of $1,500 for a sheet the size of a television screen. Also, the clear lead sheet will generally degrade the resolution of the image quality produced by the cathode ray tube. Thus, clear lead screens have not had wide application as a means of preventing the X-ray emission from cathode ray tubes.
There are a number of devices on the market today which place a screen between the cathode ray tube and the viewer. However, these screens have not been effective in preventing X-ray emission. These screens have only been used for reducing glare, preventing dust accumulation, and preventing damage to the screen. Generally, these screens are made of acrylic or other plastic that allow X-rays to pass easily therethrough. Thus, present devices which are affixed between the cathode ray tube and the viewer have been ineffective in preventing X-ray emission upon the viewer.
Polyvinyl chloride is also known in the prior art. Vinyl is the name for the univalent radical of CH.sub.2 .dbd.CH--, which is further described by its termination products as CH.sub.2 .dbd.CHR and CH.sub.2 .dbd.CHX, e.g., vinyl benzene and vinyl chloride. The divalent radical CH.sub.2 .dbd.2 is referred to as vinylidene. The various monomers that contain these structures are readily polymerized or copolymerized through their carbon double bonds. Vinyl polymers are comprised of a relatively select group, which includes polyvinyl chloride, polyvinyl acetate, polyvinyl alcohol, polyvinylidene chloride, their copolymers and related products. Polyvinyl chloride (PVC) is the exception to the limited use trend of the vinyl polymers. PVC compounds possess such dynamic versatility that they compete effectively with most thermoplastics for market applications and for available feed stocks. However, polyvinyl chloride has not had application as a radiation emission prevention device for use in combination with cathode ray tube screens.
It is an object of the present invention to provide a method and apparatus for preventing X-ray radiation emission upon the viewer of a cathode ray tube.
It is another object of the present invention to provide a radiation containment method and apparatus which is easy to manufacture and economically accessible.
It is a further object of the present invention to provide a method and apparatus that contains the X-rays emitted by the cathode ray tube while still maintaining the resolution and image quality of the cathode ray tube.
These and other features and advantages of the present invention will become apparent from reading of the attached Specification and appended Claims.